sandra - // Just take his phone and have it looked at like they would a drug dealers, and they will see how many times he's logged into such sites. //
That could only be done if the gentleman is charged with a criminal offence, the police have the power to search for evidence.
Since he has not been charged, he cannot be compelled to surrender his phone, unless it is specifically supplied as a 'work phone', in which case it may be possible to recall and examine it.
The gentleman could of course volunteer his phone for examination, but given the circumstances thus far, that's highly unlikely to occur.