Here are are two sinusoids, with slightly different frequencies, 1kHz (A, blue) and 1.2kHz (B, orange):

Even though I have not introduced any phase shift, at any time, to either, clearly the phase relationship between them changes over time. The left green marker show B slightly leading A, and the right marker shows B trailing.

Without having an identical pair of exactly the same independent signals at the receiver end (which defeats the purpose of modulating and transmitting one of them in the first place), the receiver will be unable to distinguish between a phase shift, and a frequency change.

You can't combine PSK and FSK in the same encoding scheme. Either you keep frequency fixed, and you modulate phase, or you keep phase fixed, and modulate frequency. Not both.

Here are are two sinusoids, with slightly different frequencies, 1kHz (A, blue) and 1.2kHz (B, orange):

Even though I have not introduced any phase shift, at any time, to either, clearly the phase relationship between them changes over time. The left green marker show B slightly leading A, and the right marker shows B trailing.

Without having a reference signal, perfectly sychronised with the transmitter (which would require transmitting two signals), the receiver will be unable to distinguish between a phase shift, and a frequency change.

You can't combine PSK and FSK in the same encoding scheme. Either you keep frequency fixed, and you modulate phase, or you keep phase fixed, and modulate frequency. Not both.