Organization and Description of Business	12 Months Ended
Dec. 31, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization and Description of Business	Organization and Description of Business Description of Business PhaseBio Pharmaceuticals, Inc. (the “Company”) was incorporated as a Delaware corporation on January 10, 2002. The Company is a clinical-stage biopharmaceutical company focused on the development and commercialization of novel therapies for cardiopulmonary diseases. The Company’s lead product candidate, PB2452, is a novel reversal agent for the antiplatelet drug ticagrelor, which the Company is developing for the reversal of the antiplatelet effects of ticagrelor in patients with uncontrolled major or life-threatening bleeding or requiring urgent surgery or an invasive procedure. The Company’s second product candidate, PB1046, is a once-weekly fusion protein currently in a Phase 2b clinical trial for the treatment of pulmonary arterial hypertension. PB1046 utilizes the Company’s proprietary half-life extending elastin-like polypeptide technology, which also serves as the engine for future product pipeline candidates. Liquidity The Company has experienced net losses and negative cash flows from operations since its inception and, as of December 31, 2019, had an accumulated deficit of $162.2 million. The Company expects to continue to incur net losses for at least the next several years. As of December 31, 2019, the Company had cash and cash equivalents of $74.0 million and working capital of $70.3 million. In January 2020, the Company entered into a co-development agreement ("SFJ Agreement") with SFJ Pharmaceuticals X, Ltd., an SFJ Pharmaceuticals Group company ("SFJ") pursuant to which SFJ will provide funding and operational support for the clinical development of PB2452. Management believes that its existing cash and cash equivalents as of December 31, 2019, in addition to the $10.0 million received in March 2020 and the $80.0 million in anticipated proceeds that the Company will receive pursuant to the SFJ Agreement, will be sufficient to fund operating expenses and capital requirements into the second half of 2021. The Company currently has an effective shelf registration statement on Form S-3 ("2019 Shelf Registration Statement") on file with the Securities and Exchange Commission ("SEC"), which expires January 2023. The 2019 Shelf Registration Statement currently permits the offering, issuance and sale by the Company of up to an aggregate offering price of $200.0 million of common stock, preferred stock, debt securities and warrants in one or more offerings and in any combination, of which $60.0 million may be offered, issued and sold in "at-the-market" sales pursuant to an equity distribution agreement with Citigroup Global Markets Inc. and William Blair & Company, L.L.C ("Equity Distribution Agreement"). No securities have been sold under the 2019 Shelf Registration Statement and no shares have been sold pursuant to the Equity Distribution Agreement. Basis of Presentation The accompanying financial statements have been prepared in accordance with United States generally accepted accounting principles (“GAAP”) and the rules and regulations of the SEC. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) promulgated by the Financial Accounting Standards Board (“FASB”). The Company manages its operations as a single reportable segment for the purposes of assessing performance and making operating decisions.

Organization and Description of Business

Description of Business

PhaseBio Pharmaceuticals, Inc. (the “Company”) was incorporated as a Delaware corporation on January 10, 2002. The Company is a clinical-stage biopharmaceutical company focused on the development and commercialization of novel therapies for cardiopulmonary diseases. The Company’s lead product candidate, PB2452, is a novel reversal agent for the antiplatelet drug ticagrelor, which the Company is developing for the reversal of the antiplatelet effects of ticagrelor in patients with uncontrolled major or life-threatening bleeding or requiring urgent surgery or an invasive procedure. The Company’s second product candidate, PB1046, is a once-weekly fusion protein currently in a Phase 2b clinical trial for the treatment of pulmonary arterial hypertension. PB1046 utilizes the Company’s proprietary half-life extending elastin-like polypeptide technology, which also serves as the engine for future product pipeline candidates.

Liquidity

The Company has experienced net losses and negative cash flows from operations since its inception and, as of December 31, 2019, had an accumulated deficit of $162.2 million. The Company expects to continue to incur net losses for at least the next several years. As of December 31, 2019, the Company had cash and cash equivalents of $74.0 million and working capital of $70.3 million. In January 2020, the Company entered into a co-development agreement ("SFJ Agreement") with SFJ Pharmaceuticals X, Ltd., an SFJ Pharmaceuticals Group company ("SFJ") pursuant to which SFJ will provide funding and operational support for the clinical development of PB2452. Management believes that its existing cash and cash equivalents as of December 31, 2019, in addition to the $10.0 million received in March 2020 and the $80.0 million in anticipated proceeds that the Company will receive pursuant to the SFJ Agreement, will be sufficient to fund operating expenses and capital requirements into the second half of 2021.

The Company currently has an effective shelf registration statement on Form S-3 ("2019 Shelf Registration Statement") on file with the Securities and Exchange Commission ("SEC"), which expires January 2023. The 2019 Shelf Registration Statement currently permits the offering, issuance and sale by the Company of up to an aggregate offering price of $200.0 million of common stock, preferred stock, debt securities and warrants in one or more offerings and in any combination, of which $60.0 million may be offered, issued and sold in "at-the-market" sales pursuant to an equity distribution agreement with Citigroup Global Markets Inc. and William Blair & Company, L.L.C ("Equity Distribution Agreement"). No securities have been sold under the 2019 Shelf Registration Statement and no shares have been sold pursuant to the Equity Distribution Agreement.

Basis of Presentation

The accompanying financial statements have been prepared in accordance with United States generally accepted accounting principles (“GAAP”) and the rules and regulations of the SEC. Any reference in these notes to applicable guidance is meant to refer to GAAP as found in the Accounting Standards Codification (“ASC”) and Accounting Standards Updates (“ASU”) promulgated by the Financial Accounting Standards Board (“FASB”).

The Company manages its operations as a single reportable segment for the purposes of assessing performance and making operating decisions.