Telecom-wavelength single photons are essential components for long-distance quantum networks. However, bright and pure single photon sources at telecom wavelengths remain challenging to achieve. Here, we demonstrate a bright telecom-wavelength single photon source based on a tapered nanobeam containing InAs/InP quantum dots. The tapered nanobeam enables directional and Gaussian-like far-field emission of the quantum dots. As a result, using above-band excitation we obtain an end-to-end brightness of 4.1 +/- 0.1% and first-lens brightness of 27.0 +/- 0.1% at the -1300 nm wavelength. Furthermore, we adopt quasi-resonant excitation to reduce both multiphoton emission and decoherence from unwanted charge carriers. As a result, we achieve a coherence time of 523 +/- 16 ps and postselected Hong-Ou-Mandel visibility of 0 .91 +/- 0.09 along with a comparable first-lens brightness of 21.0 +/- 0.1%. These results represent a major step toward a practical fiber-based single photon source at telecom wavelengths for long-distance quantum networks.