As an EP myself (Environmental Professional) I see absolutely no advantage to getting a geologist to perform your Phase 1. As long as you have an EP perform it, you are just fine. Having said that, you DO want someone that knows what they're doing perform the site assessment.
Even though your ESA might qualify for CERCLA protection, do you REALLY want to go through all that? Wouldn't it be better to just catch is up front while it's the other guys problem?
I just did a Phase 1 about 6 weeks ago, the gas station tanks next door leaked, contaminating the groundwater under the target property. Cleanup was ongoing for over a year and still had not been signed off on.
That was not my client's problem, but good to know up front.