Why is is it' l'on' in the question below

Hi
In the question
Avez vous un numero de telefon ou l'on peut vous joindre - is the l in front of on a prounoun?  Why is it there? Why is it not ou on peut joindre?

Thank you for any help!
Karen

Bonjour,

Good question. In this case the pronoun here actually doesn't add any meaning to the sentence, it is simply employed to avoid the clash of two vowels which ruins the flow of the sentence. This happens from time to time in French either to avoid awkwardly stretching out vowels from two different words (as in the above case) or phrases that would otherwise hit the ear wrong, such as:
     "Quoi qu'on en dise", which just doesn't sound great. Not to mention 'qu'on' sounds like 'con' which means stupid. Better to say, "quoi que l'on en dise".

I hope this helps!

   -   Marie-Claire