UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): October 22, 2018

PhaseBio Pharmaceuticals, Inc.

(Exact name of Registrant as Specified in Its Charter)

(610) 981-6500

(Registrant’s Telephone Number, Including Area Code)

Not Applicable

(Former Name or Former Address, if Changed Since Last Report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instructions A.2. below):

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§240.12b-2 of this chapter).

Emerging growth company  ☒

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act.  ☒

Item 5.03 Amendments to Articles of Incorporation or Bylaws

Amendment and Restatement of Certificate of Incorporation

On October 22, 2018, PhaseBio Pharmaceuticals, Inc. (the “Company”) filed an Amended and Restated Certificate of Incorporation, or the Restated Certificate, with the Secretary of State of the State of Delaware in connection with the closing of the Company’s initial public offering of its common stock, or the IPO. The Company’s board of directors and stockholders previously approved the Restated Certificate to be effective upon the closing of the IPO. The Restated Certificate is attached hereto as Exhibit 3.1 and is incorporated herein by reference.

Amendment and Restatement of Bylaws

Effective as of October 22, 2018, the Company adopted Amended and Restated Bylaws, or the Restated Bylaws, in connection with the closing of the IPO. The Company’s board of directors and stockholders previously approved the Restated Bylaws to be effective upon the closing of the IPO. The Restated Bylaws are attached hereto as Exhibit 3.2 and are incorporated herein by reference.

Please see the description of the Restated Certificate and the Restated Bylaws in the section titled “Description of Capital Stock” in the final prospectus the Company filed with the U.S. Securities and Exchange Commission on October 19, 2018 pursuant to Rule 424(b) under the Securities Act of 1933, as amended, relating to the Registration Statement on Form S-1, as amended (File No. 333-227474).

Item 9.01 Financial Statements and Exhibits.

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, as amended, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.