Commercial dynamically tunable lasers (DTLs) for dense wavelength-division-multiplexing optical networks are integrated devices into a butterfly package. Thus, their dimensions are much smaller than standard external cavity tunable lasers. Despite the reduced size, they present unexpected low phase noise. In this letter, the DTL phase noise is fully characterized for real-time optical coherent communication applications by using a suitable measurement technique based on an optical phase-locked loop. We experimentally demonstrate that DTLs can be used in a 10-Gb/s binary phase-shift-keying coherent optical communication system based on a phase-locking technique and a decision-driven architecture.