The post office on Phang Nga road has a public phone. Bathrooms, hygiene in general vary greatly. Guesthouses often do not have private bathrooms. The most common complaint is stomach troubles- all Thai pharmacies have over the counter medications. Remember to stay hydrated.
Condoms are available at pharmacies.
Phuket town and the major resorts have pharmacies. Don't drink unbottled or unboiled water. Ao Patang is the most popular resort on the entire island, which makes it pretty bad value for budget accommodation but who needs a bed when you can party all night long and then sleep it off on the beach the next day. Authentic, cheap eats are along the main road Soi Post Office. The next party town south of Ao Patang is Ao Karon, and at the moment there are still open stretches of beach and lower prices for accommodation and food.