Deciding on the best time to visit the Philippines is pretty straightforward. Like in other tropical countries, the Philippines only has two seasons - the rainy season and dry season.
Two Seasons of the Philippines
The Rainy Season
The Dry Season
That said, the best time to travel to the Philippines is from December to May.

Usually, the weather is good for traveling from October on. However, especially in the north of the Philippines, typhoons can arrive until November or December and make traveling uncomfortable, if not interrupted for a few days, if e.g. boat traffic has to be stopped or roads become impassable due to landslides or floods.
In the eastern provinces, heavy rainfall must be expected from November to January. But even during this time, traveling is usually not a problem.
The Philippine summer lasts from April to May. During these months you will be spoiled by a lot of sunshine, but it can get very warm, or better said, very hot. Rainfall during this time is extremely rare. On the contrary, during this time there are often bottlenecks in the water supply.
And this is also the main travel season for Filipinos. Everyone who can go to the sea and the beach. Here beaches, which are otherwise almost deserted all year round, can be completely overcrowded, especially on weekends.
From June on, the rainy season starts again. Note, though, that the start of the rainy season can also be delayed.
And in April and May otherwise lonely beaches can be completely overcrowded, when many Filipinos want to spend the hot days with their families and friends at the sea.
The time around Christmas and New Year as well as at Easter can be a bit tiring to travel, as these are the times when all Filipinos are traveling. Everyone wants to visit their family or if they can afford it, spend their vacations somewhere. At this time, there can be bottlenecks in accommodation and flight tickets should be booked early.