Going through the steps of signing based on mobile phone number I am getting: Signature cancelled by user
The improved signing flow of DocuSign and Swisscom only allows to sign based on a mobile phone number, when this number has been registered to use MobileID. Signing based on the reception of an one-time code via SMS and a personally assigned password, is now longer supported (SMS-OTP PWD).
As resolution you have two options available, which both require the step of re-identification with your national ID card or your Passport.
1.) You select to register a passkey and in future authentication with your passkey
or
2.) you register your mobile phone number with MobileID and authenticate in future via MobileID.
This change has been reflected also here
Explanation: SMS-OTP PWD base authentication is no longer considered a secure authentication means, as such we provide you with more secure means (SIM spoofing attacks). Unfortunately this change requires a re-identification (more information about the identification here: auto-identification).