2FA over SMS is stupidly bad. It's worse than TOTP in every aspect including this reason. It is also much less secure. You could start switching accounts to TOTP regardless of this and then decide if you want to switch your number later when you have the option.
TOTP is portable and can be backed up.
I went a little bit off on a tangent, the stupidity of SMS 2FA is a pet peeve of mine.
If I lose my phone I have no totp access or sms access
I walk to the local phone shop and get a replacement sim for my number with a few of bits of ID and I regain sms access. Totp access is gone forever.
It’s clearly not worse that totp in every way.
I suggest exporting your password manager && your topt keychain onto an encrypted flash drive. I went through the horrors of having a phone die on me after migrating my topt to a local solution. Having a valid login cookie on bitwarden on my laptop was the only thing that saved me.
And that post is why sms is superior.
You vans I may be able to manage a backup and understand how these codes are generated. The average person does not.
From memory most totp apps don’t even migrate when you move from one phone to another - at least on iPhone. I haven’t done that for 5 years but I seem to remember having to create new entries.