All tourists traveling to Phuket and anywhere in Thailand must possess a passport valid for at least 6 months beyond their intended length of stay (Retirement visa requires at least 18 months validity). Thailand has over 30 International Immigration Check points, though most visitors to Phuket will clear immigration either at Bangkok (Suvarnabhumi International Airport) or Phuket International Airport. For full list of international check points please see http://www.mfa.go.th/main/en/services/4908 for contact information.
For many tourists it is not necessary to apply for a visa beforehand if you come from a country that is eligible for a Visa Exemption and are not going to be in the country for more than 30 days. Other tourists may be able to apply for a Visa on Arrival, which costs 1,000 baht and is valid for 15 days. For everyone else, and for those wishing to stay longer in the country for purposes of tourism or leisure should apply for a 60-day Tourist Visa from the Royal Thai Embassy or consulate in the country where you reside.