Can I use my iPad to sign in with this iPhone after forgetting my iPhone email and password?

kaelyn823 wrote:

I need to reset my iPhone but I forgot the email and password!

Start here: If you forgot your Apple Account primary email address or phone number - Apple Support

Also: If you forgot your Apple Account password - Apple Support

Can I sign into my iPad with this phone?

No. If you used the same Apple Account in both, you can look up account details on either.

If different Apple Accounts were used, and if the Apple Account associated with the iPhone is unavailable for whatever reason, the reset will not clear Activation Lock, and the iPhone won’t be useful.

Reset passcode with a computer: Use a computer to reset your iPhone and your passcode - Apple Support

Reset without: If you forgot your iPhone, iPad, or Apple Vision Pro passcode, reset your device without a computer - Apple Support

Again, resetting the passcode will not bypass or remove Activation Lock. In general, what amounts to a transfer needs access to the account, or needs the account holder remotely remove the lock, or needs proof of ownership sufficient to convince Apple — such as an original purchase receipt from Apple or an authorized reseller.