POWER OF ATTORNEY

      Know all by these presents, that the undersigned hereby
constitutes and appoints Anne T. Leland, Brenda L. Meyette, Jacquelyn
A. Cannata, Megan N. Gates, Peter N. Cunningham, Verna Krishnamurthy
and Hana M. Sahdev of Mintz, Levin, Cohn, Ferris, Glovsky and Popeo,
P.C., and J. Stillman Hanson, Jennifer K. Moses, Becky Daniel and
Sandi James of G1 Therapeutics, Inc. signing singly, with full power
of substitution, the undersigned's true and lawful attorney-in-fact
to:
	(1)	execute for and on behalf of the undersigned, forms and
authentication documents for EDGAR Filing Access;

(2)	do and perform any and all acts for and on behalf of the
undersigned which may be necessary or desirable to complete
and execute any such forms and authentication documents;

(3) 	execute for and on behalf of the undersigned, in the
undersigned's capacity as an officer, director and/or 10%
shareholder of the Company, Forms 3, 4 and 5 in accordance
with Section 16(a) of the Securities Exchange Act of 1934
and the rules thereunder;

	(4)	do and perform any and all acts for and on behalf of the
undersigned which may be necessary or desirable to complete
and execute any such Form 3, 4 or 5 and timely file such
form with the United States Securities and Exchange
Commission and any stock exchange or similar authority; and

	(5)	take any other action of any type whatsoever in connection
with the foregoing which, in the opinion of such attorney-
in-fact, may be of benefit to, in the best interest of, or
legally required by, the undersigned, it being understood
that the documents executed by such attorney-in-fact, on
behalf of the undersigned pursuant to this Power of
Attorney, shall be in such form and shall contain such
terms and conditions as such attorney-in-fact may approve
in such attorney-in-fact's discretion.

	The undersigned hereby grants to each such attorney-in-fact full
power and authority to do and perform any and every act and thing
whatsoever requisite, necessary, or proper to be done in the exercise
of any of the rights and powers herein granted, as fully to all
intents and purposes as the undersigned might or could do if
personally present, with full power of substitution or revocation,
hereby ratifying and confirming all that such attorney-in-fact, or
such attorney-in-fact's substitute or substitutes, shall lawfully do
or cause to be done by virtue of this power of attorney and the
rights and powers herein granted.  The undersigned acknowledges that
the foregoing attorneys-in-fact, in serving in such capacity at the
request of the undersigned, is not assuming, nor is the Company
assuming, any of the undersigned's responsibilities to comply with
Section 16 of the Securities Exchange Act of 1934.

	This Power of Attorney shall remain in full force and effect
until the undersigned is no longer required to file Forms 3, 4 and 5
with respect to the undersigned's holdings of and transactions in
securities issued by the Company, unless earlier revoked by the
undersigned in a signed writing delivered to the foregoing attorneys-
in-fact.

	IN WITNESS WHEREOF, the undersigned has caused this Power of
Attorney to be executed this 4th day of September 2018.

					/s/ Barclay A. Phillips
					Barclay A. Phillips