The one area I'd maybe be a bit wary of using your Ph.D 'Dr' is in fact in a medical setting as there can be an assumption that you're 100% clued up thus won't get the explanation s, in layman's terms, of what's going on!
A fortnight ago, I performed a medical scan upon a bloke, Mr so-and-so, complete with my layman's, though not simplistic explanation of what the cannula and drugs were for, all fine, then when we finished, he began to unpeeled the dressing from the cannula, so I went 'Hang on, wait a sec!', fearing a haemorrhage 😁 but he then admitted he was a consultant neurologist! He said that his reason for not saying initially was so he'd get the full explanation as he knew little about the type of scan I was doing or the organ I was scanning, beyond being 2-3 years qualified!
I get that. A dermatologist is not a radiologist, who is not an endocrinologist.
In fact, we still eyeroll a bit when you say ' Hello, Mrs So-and-so' and they go 'Its Dr So-and-so' as the implication is that we'd otherwise patronise you...... And, anecdotally, you are often the ones who haven't read the test instructions properly, or don't know exactly what or why you've been sent for the test ('Sorry, Dr So-and-so, that's a conversation you should have had with your consultant, not me!').....