If Digital Replays with no concerning issues.
Use the Power Amp's Digital Input as the Phon's PH 10 Input, and use the Digital Input at the Phon's Input.
If the problem Phon's Issue migrates across the Inputs, then the Problem will be looking most likely to be upstream of the Power Amp.
Can the PH 10 be bypassed to see if it has a issue, Is there another option to use in place of the PH 10.
Does the Amp Set Up have a Phono Input ?
Use the Power Amp's Digital Input as the Phon's PH 10 Input, and use the Digital Input at the Phon's Input.
If the problem Phon's Issue migrates across the Inputs, then the Problem will be looking most likely to be upstream of the Power Amp.
Can the PH 10 be bypassed to see if it has a issue, Is there another option to use in place of the PH 10.
Does the Amp Set Up have a Phono Input ?