"Can i manage it with QOS?"
Possibly - much depends on the platform.
Some platforms will allow an ingress policy where you can examine the traffic and remark, if desired. BTW, you might do this based on IP address, or perhaps on other attributes (e.g. traffic that "looks" like VoIP).
Another approach is to have the VoIP phones mark their own traffic and then you trust those markings. That, though, opens you up to potential abuse, i.e. other traffic could self mark itself like VoIP traffic. What you can also do is "trust but verify", i.e. use a policy that will only accept traffic with VoIP ToS markings that "looks" like VoIP traffic. Also, and/or, some platforms allow policies that can rate limit traffic. You might, for example, cap "VoIP" ingress traffic (from a VoIP phone) at about 100 to 150 Kbps. (Using just a rate limiter, without further traffic analysis, at least precludes excessive "abuse". For example, a FTP flow, self-marking with VoIP ToS tags would only get a small amount of bandwidth to use.)
