What is the phase variation in amplifier with linear and saturation condition ?

I m using the HMC741 Amplifier in my receiver chain. Here i m trying to find the phase difference between input and output with different input power levels . In this chain only HMC741 Amplifier is going to saturation region with high power input level. At the high power condition, the measured phase value is changing. 

So, What is the phase variation in amplifier with linear and saturation condition ?