A series of 2-phenylpyrimidine coumarin derivatives with potential telomerase-inhibiting activity was designed and synthesized. All of the compounds were screened for antiproliferative activity against CNE2, KB, and Cal27 cell lines in vitro. The results showed that most of the derivatives had a favorable effect on resisting tumor cell proliferation; compound 13, 3-(4-amino-5-oxo-5H-chromeno[4,3-d]pyrimidin-2-yl)phenyl 4-(dimethylamino)benzenesulfonate, exhibited the best activity. Flow cytometry revealed that compound 13 can inhibit CNE2 proliferation. Telomerase inhibition and in vitro antitumor activity were consistent among the compounds, but compound 13 showed the best telomerase-inhibiting activity and could inhibit telomere extension. Molecular docking results indicated that compound 13 bonded with telomerase reverse transcriptase (TERT) through multiple interactions, including hydrogen bonding and hydrophobic interactions. The results of the study provide further information on 2-phenylpyrimidine coumarins, expanding the types of telomerase inhibitors as the parent structures.