Digital Signature on cell phone

Do you mean digital or electronic signature?  There is a difference.

For electronic signature, see e-Sign mobile app.

https://acrobat.adobe.com/us/en/sign/features/e-sign-mobile-app.html

For capturing a reusable signature from your mobile app, see below.

https://helpx.adobe.com/acrobat/using/capture-and-sync-your-signature.html

I don't use a cell phone for that, but asking in one of these forums might help

https://community.adobe.com/t5/acrobat-reader-mobile/bd-p/acrobat-reader-mobile?page=1&sort=latest_replies&filter=all

or

https://community.adobe.com/t5/adobe-sign/bd-p/adobe-sign?page=1&sort=latest_replies&filter=all