I think disclosing your stutter is super important, especially if you're struggling. Takes a massive weight off your shoulders and gives the listener a bit of clarity about why you may be struggling. In regards to phone calls, I used to practice just ringing stores, gas stations etc, and asking them basic questions (e.g. what time do you close?, when are you opening tomorrow?) purely for the sake of overkilling the fear I had with telephone calls. Once this is easy you can also add in some more challenging words which may challenge you a bit more. In regard to talking to new people, I sometimes just walk around my local shopping centre and try and strike up a conversation with shop clerks and people walking around purely for the sake of practice. You can challenge yourself more with this and add in challenging words too. I have often found if you disclose your stutter and tell them you are speaking to them for speech practice, they are often super receptive and will happily have a conversation with you (I had some that went for half an hour sometimes). This is also a good opportunity to say your name and introduce yourself to people, which is exactly replicating a real introduction scenario. Hope this helps!