I am not sure which excel function to use.

I need to create a formula that looks for a # in a cell and returns a
corresponding person's initials. If there are multiple occurences I need to
concatenate the initials into one cell separated by a comma.

In row 1, i have the person initials
In row 2, I have the #'s
In row 3, the formula

Therefore,

A B C D E
1 PH IS CF MS AS Row 1

2 # # # Row 2

The formula result in row 3 should be PH,CF,AS

Can anyone help?
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J