Bakelite Synthesis
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It is not actually the phenol but the phenoxide ion (formed due to the weak acidity of phenol) that is the reactive species.
The electron-deprived C of formaldehyde adds to the phenol ortho or para to the oxygen, since these are the spots where resonance structures can be drawn to give a formal negative charge.
We can lose OH- from the substituent (so we end up with one H2O per formaldehyde, and a technical condensation).
Then there are a lot of arrows moving around, and what it looks like is a carbanion addition to a double bond....
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