While Fools should generally take the opinion of Wall Street with a grain of salt, it's not a bad idea to take a look at particularly stock-shaking analyst upgrades and downgrades -- just in case their reasoning behind the call makes sense.

What: Shares of Phillips 66 Partners (NYSE:PSXP) sank 4% on Wednesday after Credit Suisse downgraded the petroleum refiner from outperform to neutral.

So what: Along with the downgrade, analyst John Edwards planted a higher price target of $47 on the stock, representing just 2% worth of upside to yesterday's close. While momentum traders might be attracted to the stock's sharp surge in recent months, Edwards thinks that much Phillips' growth prospects are already baked into the valuation.

Now what: According to Credit Suisse, Phillips' risk/reward trade-off is pretty balanced at this point. "PSXP has delivered total returns of ~25% in the first two months of 2014, far ahead of the sector average and leading the pack for midstream MLPs," noted Edwards. "While we remain entirely confident in PSXP's growth story, de-risked cash flow and 22% 3-year distribution CAGR, we believe the current stock price fairly reflects its growth potential." With Phillips sporting a pricey forward P/E of 25 and a sector-lagging yield below 2%, it's tough to disagree with Credit Suisse's cautious stance.  

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.