I have two large columns, one 391k long and one 50k. I need to have the cells with the same data put next to eachother

I have two large columns, one 391k long and one 50k. I need to have the
cells with the same data put next to eachother

Both columns A & B have phone numbers. Each of the 50,000 column B does
appear in the column A with 391,000 too.
I just want the 50,000 column B to have each number matched up with the
same ROW as the 391k column A.
This way the same row for both column A and column B have the same value
if the data is in both rows. If there is a phone number on the 391k list,
but not on the 50k list, then in that row, column A would have a phone
number, and column B would be blank.