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Ah, righto. What about a USB-C (assuming your phone is USB-C) adapter to USB-A and then plug the dongle in? I've never tried that (my old Sony had native ANT+ support) but maybe you could give something like that a go? Seems unlikely it'll work unless a phone app can use ANT+ that way.
Regarding the bluetooth - dodgy how? I presume you've paired it? Have you disabled other BT devices nearby?
ANT+ dongles are cheap aren't they? You might get further with one of those?