|You could but then as has been stated, you'll never be able to use all 8 pairs on a network cable and would therefore be limiting yourself to a 100 Mbps maximum bandwidth. 1000 Mbps (1 gig) uses all 4 pairs.|
Check with your builder and the electricians. It could be the plan is to pull separate cables for phone and network utilizing Cat6 for both. So instead of a single cable, two.
We use Cat5e for phones a lot where I work and use separate cables pulled with the network cables. This allows up to 4 telephones on one cable (phone only uses 1 pair).
As far as houses go, you won't save much on cabling if the plan was 2 cables per room (1 phone, 1 data) and you tell them not to pull the one for the phone.
So, if the plan is, a separate cable for phone, I'd just leave it as is.