Yes, you will receive a new telephone number when you purchase this SIM card. If you want to keep your existing number, you must indicate this when placing your order (number porting). If you do not specify this, a new number will be assigned.
It's best to contact our colleagues from the mobile team directly so that they can solve your problem straight away and everything is stored correctly:
https://helpcenter.mobile.galaxus.ch/hc...
If you switch to Galaxus Mobile, you must state when ordering your SIM card that you want to keep your existing mobile number (number porting). Then it's sure to work.