more phlox questions and bugs/slugs nearby

[AnimalBabe]

Hi all, I bought phlox for the first time this spring and was wondering if I could trim it back and have it rebloom. If I can trim it, how far do I go, and do I just cut off the whole top inch or so??

Also, I have some zinnias growing nearby and found some circular cut outs on their leaves. I was looking around for possible bugs and also noticed some slugs living on the underside of the phlox. What would you recommend I do about either?
Thanks for your help!