Alphabet Inc.’s Google is killing plans to make a modular phone, according to two people familiar with the project, the end of an ambitious internal program to reinvent smartphones.

The company told partners in the past week that it was ending its three-year-old Project Ara, which aimed to develop smartphones with modular, replaceable parts that snap onto its back, one of the people said. Ara’s end is part of a larger reorganization of Google’s hardware team under new hardware chiefRick Osterloh that intends to narrow its...