The most obvious one: both are Southeast Asian countries. If you pick a random Thai and random Filipino, you might not be able to tell which is which. They have similar features (complexion, built, facial features, black hair).
Which picture features Filipinos/ Thai?
If you are unfamiliar with the language, you might also think Thai and Philippine languages sound alike. They have same inflections, the sing-song tone of speaking. But the similarities are superficial since Thai belongs to the Tai-Kadai language family while Philippine languages originate from the Austronesian (Malayo-Polynesian) family.
Both countries are blessed with beautiful beaches and islands that are quite popular tourist spots.
That’s all I could think of for now. The two countries look similar but they have also many fundamental differences (religion: Buddhist vs. Christian; Philippines has a long colonial history while Thailand does not; English is more widely spoken in the Philippines).