You Do Need power plug adapter while traveling from Philippines to Guam.

Here is Why You Need An Adapter

The outlet and plug type used in Guam are A and B and in Philippines are A, B and C. This is how they look like.

Philippines

In Philippines, outlets of type A, B and C are in use.

Type A

Type B

Type C

Guam

In Guam, outlets of type A and B are in use.

Type A

Type B