Identify the name of reaction when phenol reacts with chloroform in aqueous NaOH.

When phenol is treated with chloroform ($CHCl_3$) in the presence of aqueous sodium hydroxide ($NaOH$), an aldehyde group ($-CHO$) is introduced at the ortho position of the benzene ring. This reaction results in the formation of salicylaldehyde (2-hydroxybenzaldehyde) as the major product.

This electrophilic substitution reaction, which proceeds via a dichlorocarbene ($:CCl_2$) intermediate, is known as the Reimer-Tiemann reaction.

Answer: Reimer-Tiemann reaction