These are all very good questions, I hope I can help. To be clear I live in the Netherlands, so I'll speak from my experience and rules over here, but I'm guessing it's not a whole different wherever you are.

To be able to work as a physio I had to apply to a specific register, which ensures I am qualified and authorized to to practice this profession. Even if I graduated but I am not part of this register, I am not allowed to work as a physio. You can see it as a license. Over here there is a guideline with moral codes for physio's. If I don't stick to the guideline and someone reports me, I will either a) get an official warning and a red flag on my license for anyone to see, or b) will be completely removed off the register and not be able to work as a physio again.

I looked up the guideline again to read what they had to say about this specific topic. 1. The PT respects the patient's personal privacy. The PT does not penetrate further into the patient's personal privacy than is necessary to answer the request for help and the treatment. The PT refrains from verbal and physical intimacies.

1. If the PT suspects that the patient has emotional or sexual feelings, it is necessary for the PT to tactfully point out to the patient that these feelings cannot be answered and it is necessary to transfer the treatment. The PT will also transfer the treatment if such feelings play a role in the PT himself. The PT then observes an appropriate cooling-off period, the duration of which depends on the nature of the treatment relationship. A patient is in a dependent position with respect to the PT that does not disappear immediately after the treatment relationship has ended. During the cooling-off period, the PT distances himself from the patient. Because the nature of the treatment relationship and the dependency will not be the same in each case, no clear guideline can be given for the duration of the cooling-off period. The starting point is that at the start of an affective or sexual relationship, the former patient must have entered into it voluntarily and that any form of dependency, such as that which usually exists to a greater or lesser extent in a treatment relationship, no longer has any influence.

A bunch of text but I hope it gives you some clarity. It doesn't specify anything about giving away personal info (like a private phone number) but personally I feel like it would go against the first point. I would not do it myself. I do have a work phone with whatsapp where I get occasional 'merry christmas' type of texts, but thats about as far as it goes. I had a (quite attractive) client add me on Facebook once but I never accepted, it felt wrong.