Follow the road off the main road next to Yuhoua Guesthouse down the hill and you'll see the tourism office about 100 metres in front of you.
If you're interested in going trekking or seeing some of Phongsali's surrounds, it's worth the effort of tracking down.
Inside the official Provincial Tourism Office they have information on a wide range of treks in the vicinity, ranging from short one-day hikes to multi-day affairs that include visits and overnight stays in local villages including ones home to Phou Noy, Akha, Lao Seng, Lue and Ho ethnic groups. This region is fairly untouristed, so for the villages on each route it will be a relatively uncommon experience to have foreign visitors.
Cost depends on the number of people going, starting at one person for 500,000 kip per day although this should be negotiable. Price covers accommodation and transport, an English-speaking guide, and all meals, which are basic.
Disappointingly, the tourism office isn't interested in helping trekkers freestyle it into the surrounding hills, so if you want to do this, you may well need to ask locals for some information, but given the lack of English spoken in town, this could end up being quite a challenge.