Cleaning Up Phone Number Lists?

I have an old customer list maintained by my company's previous owner in excel format that mostly stored numbers ###-#### format, but also some in ###-###-#### format.

My new list has always been maintained with numbers in (###) ###-#### format.

I have merged these two lists in a new excel file have begun the tedious process of cleaning up duplicates and bad data.

I have used conditional formatting to highlight duplicate numbers in the appropriate columns (L, M, N, O) in this case. However, it does't find matches in the other formats or perhaps the number with the old area code. I know the area code change could lead to false positives, but they should be minimal as this is a small business with mostly local customers. So what I'd like to find out is a formula for conditional formatting that will compare the last 8 characters in each cell (###-####) so as to eliminate issues of missing or different area codes. I would like it to check all of the columns for duplicate numbers not just within each column or within each row individually.

Also separate but related if possible to highlight a different color any cells with data not in any of these formats or if not in (###) ###-#### format if it's too much for all the formats.