Firstly, for safety reasons, it's crucial not to use the phone anymore and to keep it away from heat or pressure. Apple does take issues like this seriously due to safety concerns, so it's advisable to contact Apple Support immediately or visit an authorized Apple service provider to get assistance. If your husband's phone is under warranty or covered by AppleCare, they might offer a replacement or repair.
Sometimes, issues like this can occur due to battery wear and tear. Nonetheless, reaching out to Apple Support or visiting an authorized service provider is the best course of action to ensure your husband's safety and to resolve the issue with the phone.
If you feel that Apple isn't addressing the problem adequately, it might also be helpful to escalate the issue through their customer support or visit an Apple Store to discuss the situation in person. Keeping records of your interactions with Apple support can also be beneficial in case further action is needed.