I included the following sentence in a document draft: "I built a new query to pull a list of existing customers to use as a prospecting list for cross selling collaboration solutions." A reviewer of the document responded saying I was "mixing tenses within the sentence". I went to the internet and entered the sentence into a grammar checker, which identified no errors. I don't see any tense errors.

Based on a response to a previous grammar question, I believe I have two infinitive phrases (starting with "to"). Yes.

Can somone clarify the situation with the final phrase (starting with "for"). I think it is a prepositional phrase. Yes.

I have been attempting to research verbs on the interent and I think I have the -ING participle verb form. Am I correct or totally off base? 'Cross-selling' is a gerund, and it is used correctly. You could just as easily say 'for cross-sales of  collaborative solutions'.

Although there are no grammar errors, here's my advice. Avoid sentences like this that string several of these long phrases together. It gets to be hard work for the reader to understand your meaning, and it makes what you are saying sound 'weaker'.

Compare this.

 "I built a new query to pull a list of existing customers . We can prospect with this, in order to cross-sell collaboration solutions."

Best wishes, Clive