PHP form mail will not return entries with @yahoo.com address
If youre sending mail From an arbitrary address this will almost surely get blocked as this is called spoofing and is easily detected as illegitimate.
You need to send from an address you own and control.
Yahoo is very strict about SPF records and particular about DKIM, so ensure both of those are set up and validate correctly.
Whenever you set up an email form tool, be absolutely certain that someone cant hijack this to send arbitrary content to arbitrary addresses. If this is possible someone will inevitably discover this and use it to send out unsolicited mail.