Over the past year or so, I've taken to chucking my phone in a drawer (off or on, off when I'm super angry and want to spew vitriol at my bf ) and leaving it there for hours... I leave the house, and do my best to forget it exists.
It has become easier to do, because its helped me to feel empowered. As said above, it definitly is a way to feel and be less stressed, secondly, when thAt text or call does come through, I go "sorry I missed your call babe I was busy, maybe next time"...

do you have any idea how frucking fantastic that feels???
To be the one with the power to make or break plans, instead of the one helplessly waiting for the phone to ring or dialling his number incessantly like a bloody lunatic?
Its Omgawesome!!!
This has not been an easy practice to partake in, at first I could only go an hour max without retrieving my phone, but it gets easier each time, and now I manage to go for long stretches without my phone. Thus I experience longer stretches free of obsessing.
And over time, it does become a more natural response, and doesn't feel forced at all.
I unfortunately have no advice wrt strangers, I've never become hung up on someone I don't know, not since after age 15 anyway... Sounds horribly rough though

I know it would bring a whole different level of turmoil for me as it would automatically include a shyt ton of self-loathing for me personally.
I hope you learn how to deal with this effectively soon.