lookup_value = The value (phone number) you want to lookup.
table_array = The table of content containing the value.
col_index_num = The column number which contains the value (name) you want to retrieve.
range_lookup = [optional] false: find the exact value. True or empty: find the closest match.
Now you might understand why I wanted you to rearrange you data like:
06123456789 - Henkie
06987456321 - Jopie
06789654123 - Kees
Henkie - 06123456789 - Henkie
Jopie - 06987456321 - Jopie
Kees - 06789654123 - Kees
Since the data you want to lookup needs to be in front of the data you want to retrieve.
So on your second sheet you have a list (eg. column D) of phone numbers. Insert an empty column next to them.
Then your formula would look like this:
So D1 contains the phone number you want to look up.
Sheet1!$A$1:$B$3 contains the list of phone numbers and names.
The number 2 tells excel to retrieve the data from the second column.
FALSE: find exact match.
The $ signs makes the array absolute, which doesn't change the array when dragged down.
Hopefully this makes sense.
Feel free to ask if something is still unclear.