What is the name of the process that changes the phase angle of an RF signal to convey information?

Phase modulation (PM) is a form of angle modulation where the phase angle of a radio frequency (RF) carrier wave is varied to encode and transmit information. As the modulating signal's amplitude changes, the phase of the carrier is shifted accordingly. Phase modulation is very closely related to frequency modulation (FM); in fact, phase modulating a carrier produces a form of frequency modulation, which is how many analog FM transmitters actually work under the hood. The other options, like phase inversion or convolution, refer to entirely different signal processing or mathematical techniques.