The phallic symbol. That is correct. It is the image of the penis, which is venerated in religions such as ours as symbolising the generative force in nature.
15 seconds sound clip from the The Wicker Man (1973) movie soundboard.
You can hear this line at 00:25:51 in the Blu-ray version of the movie.
Quote context
[...]
- Now, uh, Daisy, will you tell us what it is, please, that the Maypole represents?
- Really, Daisy. You've been told often enough.
- Could I have a word with you, please, Miss?
- Girls, open your desks and take out your exercise books.
- Miss, you can be quite sure that I shall report this to the proper authorities.
[...]