Organization and Description of Business	6 Months Ended
Organization and Description of Business	Jun. 30, 2020
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 in Phase 2 development for the treatment of pulmonary arterial hypertension ("PAH") and in a Phase 2 clinical trial for the treatment of hospitalized COVID-19 patients at high risk for rapid clinical deterioration and acute respiratory distress syndrome ("ARDS"), which the Company refers to as the VANGARD trial. PB1046 utilizes the Company’s proprietary half-life extending elastin-like polypeptide technology, which also serves as an engine for the Company’s preclinical pipeline. The Company is also developing its preclinical product candidate, PB6440, for treatment-resistant hypertension. Liquidity The Company has experienced net losses and negative cash flows from operations since its inception and, as of June 30, 2020, had an accumulated deficit of $205.2 million. The Company expects to continue to incur net losses for at least the next several years. As of June 30, 2020, the Company had cash and cash equivalents of $53.0 million and working capital of $45.9 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 June 30, 2020, in addition to the $2.4 million received in July 2020 through the issuance of common stock under the Company's ATM Program (as defined below) and the $71.6 million in anticipated services and 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 in 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. (the "ATM Program"). The Company is continuing to assess the effect that the COVID-19 pandemic may have on its business and operations. The extent to which COVID-19 may impact the Company's business and operations will depend on future developments that are highly uncertain and cannot be predicted with confidence, such as the geographic distribution of the disease over time, the efficacy and availability of vaccines and antiviral agents against the disease, the continued duration of the outbreak, the duration and effect of business disruptions and the short-term effects and ultimate effectiveness of the travel restrictions, quarantines, social distancing requirements and business closures in the United States and other countries to contain and treat the disease. While the potential economic impact brought by, and the continued duration of, COVID-19 may be difficult to assess or predict, a continued and growing pandemic could result in significant disruption of global financial markets, reducing the Company's ability to access capital, which could in the future negatively affect its liquidity. In addition, a recession or market correction resulting from the spread of COVID-19 could materially affect the Company's business and the value of its common stock. Basis of Presentation The accompanying condensed financial statements have been prepared in accordance with United States generally accepted accounting principles (“GAAP”) for interim financial reporting and the rules and regulations of the SEC. Certain information and note disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to those rules and regulations. All adjustments, consisting only of normal recurring adjustments, necessary for a fair presentation of the accompanying condensed financial statements have been made. Although these interim condensed financial statements do not include all of the information and footnotes required for complete annual financial statements, management believes the disclosures are adequate to make the information presented not misleading. The unaudited interim results of operations and cash flows for the three and six months ended June 30, 2020 are not necessarily indicative of the results that may be expected for the full year. The unaudited interim condensed financial statements and footnotes should be read in conjunction with the audited financial statements and footnotes for the year ended December 31, 2019, included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019, filed with the SEC on March 30, 2020, wherein a more complete discussion of significant accounting policies and certain other information can be found. 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”). Certain non-significant reclassifications have been made to conform the prior period presentation. The Company manages its operations as a single reportable segment for the purposes of assessing performance and making operating decisions.