QOS for Voip

I have the following Dell Switches:

3548P, 3524P, & 3448 (Not doing any stacking)

Using a Fonality phone server with Aastra phones.  The phones can add add the DSCP info.  Computers will be attached to PC port on the phones as we don't have enough data ports in each office.

Since the phones support DSCP, would enabling Quality of Service with DSCP Trust Mode be a good starting point to prioritize the VOIP traffic?  What should I look for in the Switch statistics to check for network congestion?