Unfortunately or not, there is no escaping bentching on Shabbat. You've gotta eat challah! Do your best to locate a bentcher with English or transliteration. Just about every host should have at least a couple bentchers with English, but you can also ask for a siddur with English. Bentching will be listed in the table of contents under "Blessings" or something similar. However, it's possible you might end up in a house with both Hebrew-only bentchers and siddurim (it happened to me once, and boy was that awkward). In that case, do the best you can. In the future, you can bring a siddur or bentcher with you (assuming there's an eruv) or drop it off before Shabbat. If you carry around your own siddur, no one is going to think you're strange. They might just think you're fresh off the boat from seminary or yeshiva in Israel.
The irony is that frequent bentching is the key to faster bentching, and thus, losing your bentchophobia.