Phones TPM speak PKCS11. As long as you're willing write in the native language (Kotlin or Objective-C), and the TPM lists EC as a supported feature (they all do RSA but EC is present maybe 50% of the time?), then you can do hardware exponentiation and signing. Vaults on phones are "fairly" well implemented from my experience, the material is correctly enclaved to the binary that created the entry, and with the proper options at creation, it will never reveal the private data.

Phones as a primary hardware wallet are useless, but as a secondary signer in a multisig scheme, why not?