Good morning @manfret I have that exact setup on my android phone. I set it up in the phone app. In the keypad screen, open the settings by using the 3 dot menu on the upper right hand side. Scroll down to voicemail, open that, then tap on voicemail number. At the end of the number add a comma, type in your numeric password followed with the number sign.
Example: +15777370210,xxxx#
It may be similar on the iPhone
