I am traveling to Dominican Republic. Can I use my phone?

usually it depends on your plan.

https://www.t-mobile.com/cell-phone-plans/international-roaming-plans?icid=MGPO_TMO_P_TMOTRVLBNF_TD9F4G9464MO28R29943

per the search though it says they do not have coverage there however do have coverage in DR or at least parts of not including Santo Domingo.

i did find this thread from a couple years ago for the same area though

from what i can see your thread here and the one i posted for that area of DR are the only two threads ever posted in here lol.

Assuming that you have a fairly modern postpaid plan, your phone should work in DOMREP. Calls will be 25¢/min and data may be throttled to ~256 kbps. Here are my hints for cost effective international roaming.   https://www.t-mobile.com/cell-phone-plans/international-roaming-plans?country=Dominican%20Republic