Can the police keep my cell phone even though the entire ad is based on my testimony?

The cell phone and laptop were taken from me because of the SMG and after the procedure I should get my laptop back but the cell phone remains confiscated. Although the entire display is based on my statement and virtually no evidence was found on the device. The only reason why this cell phone still existed was because I had not saved the pictures from the past 2 years. Then our friend and helper intervened.

Yes, she can.

I don't know if I can compare it, but I also showed someone based on text messages / photos, etc., which also went to court - however, I didn't even have to hand in my cell phone after the search…

Frankly, I can't really judge whether you have the right to get it back, but if you're the accuser, I see no reason to recover your belongings after the trial.

Apart from that, yes the police can keep your cell phone…

The return of confiscated or seized items is based on § 111n StPO.

If the device is obviously no longer required for the procedure, it must be returned.

The obviousness is at the latest when the procedure is over and the time limit for appeal has expired.

An "eternal" removal of the cell phone is therefore not permitted.