An effort is being made to upgrade the Advanced Photon Source Linac rf phase detector system. The decision was made to replace the current phase measurement system, which is based on a Los Alamos designed analog vector detector module, with a digital I/Q method. As an initial step we reconfigured one of our current 8-channel, 14-bit ADC designs, originally developed for the storage ring beam position monitor system, to perform the I/Q sampling and the phase and magnitude computations. This paper discusses the current board design, proposed modifications to optimize the board for this application, and field programmable gate array design.