But laws limit the output. I only know this area a little so you look for hearing aid compatible phones like https://www.google.com/search?hl=en&as_q=cell+phones+that+are+hearing+aid+compatible
Need cellphone for user with severe hearing loss. Prefer smaller unit than I-phone 6 and I only use phone function--no texting, etc. Note I-phone six rated at 100 decibels with speaker engaged; would like this amplification with smaller unit--flip phone OK.