When formaldehyde reacts with phenol under alkaline conditions, it undergoes a polymerization reaction known as phenolic resin formation. The alkali acts as a catalyst, facilitating the condensation between the carbonyl group of formaldehyde and the ortho and para positions of the phenol ring. This stepwise reaction produces a cross-linked, thermosetting polymer.

The chemical structure involves repeated units of $C{H}_2$ bridges between phenol molecules, forming a robust and insoluble material. This specific polymer is commercially and historically significant.

Final Answer: bakelite