This isn't true in practice. It's not hard to build a big list of ~every email address (give or take), and have a GPU churn through them all until you get a match.
If you've ever received a spam email, your email address is on such a list.
If equality-check is required to prevent e-mail reuse by spammers then argon2id with static salt rotated every few months will be reasonably strong too.
Of course I have no idea if any of this is implemented or it's just sha256(email). Just replying to the question of general feasibility.
I've no reason to doubt this but brute-force cracking a hash known to be from a phone number would likely be pretty trivial.
Fwiw, I use protonmail and trust it more than most other services. But my threat model doesn't involve technically capable adversaries directly targeting me, certainly not ones that could compel protonmail to divulge phone number hashes.
While we did use phone verification in the past, this is not the case any longer. Phone numbers were stored in the same way as the email addresses, so, again, we have no way to derive them back from the hash.