using my voicemail instead of the answering system

You can set up smart call blocker so only those calls go to your answering machine. So you can leave the answering machine on and those in your directory and star list will go to your voicemail. Read through your blocking options.

spoom2 - I can see there are 5 profile options available. It's not clear to me which option will let me do what you say:

allowed calls to voicemail

unknown calls to answering machine

Give me your make and model of phone as there are differences. 

Complete user’s manual
CL83519
DECT 6.0 cordless telephone/
answering system with
caller ID/call waiting

3. Press qCID or pDIR to select one of the following options,
then press MENU/SELECT.

1 Screen unknown - screen any calls without numbers or with numbers
not saved in the Directory, Allow list, or Star name list.
- This profile setting sets the telephone to screen all unknown calls and asks the callers to
say their names before putting the calls through to you. See Screen unknown calls on

2 Screen robot - screen robocalls.
- This profile setting sets the telephone to screen all unknown calls and asks the callers to
press the pound key (#) before putting the calls through to you. See Screen robocalls
on .

3 Allow unknown (default setting) - allow all unknown calls to ring,
except calls with numbers saved in the block list.
- This profile setting sets the telephone to allow all unknown calls to get through and ring.
Calls with numbers saved in the block list will be rejected.

4 UnknownToAns.S - forward all unknown calls to the answering
system.
- This profile setting sets the telephone to forward all unknown calls to the answering
system.

5 Block unknown - block all unknown calls.
- This profile setting sets the telephone to block all unknown calls.

Number 4 should work than set your answering machine to a greater number of rings than your voicemail.