Welcome to the community, @Andrew_Roche!
There are a few issues with the formula you wrote. First all, all quotes need to be non-styled quotes. The forum automatically styles quotes in normal text, which is why it’s preferred to format formulas using the preformatted text option. This can be done by selecting the formula and clicking the preformatted text icon: </>
When properly formatted, quotes should be straight vertical quotes, not slanted or curly. Airtable won’t recognize the latter type.
It also looks like you’ve got an extra level of parentheses around your condition check, which is likely causing part of the problem. The beginning portion should look like this:
IF({Keyphrase}=BLANK(), ...
However, you can simplify the way you look for the {Keyphrase}
field’s contents by only listing the field name:
IF(FieldName, result_if_true, optional_result_if_false)
Anything in that field is equivalent to true, and an empty field is equivalent to false.
With that applied and the parentheses and quote issues fixed, this should work:
IF(Keyphrase, LEN(Keyphrase) - LEN(SUBSTITUTE(Keyphrase, ",", "")) + 1, 0)