Try https://crypton.sh - they do exactly that

But better would be to stop using crappy applications that require a phone number to begin with

Looks like they are out of all the plans that actually give you a phone #.  They do have plans that are data only though.  Very cool stuff.

I'd love a service that you can buy numbers/esims and just have them in a portal that you can pick and choose which ones you want to use.  This would help with things like discord where you have to have a phone number tied to your account.