Don’t worry. Almost everyone in Portugal speaks Portuguese. You’ll be surprised about that.
I wish you a nice stay.

i found it a bit difficult to speak english in Lisbon. I did find a few stores with people who spoke english, but not too many.

It should be fairly easy, I would recommend buying a small phrase book. Try to memorize a few phrases you know you will use often, for me it was ordering coffee with milk. I also learned to say please and thank-you and almost everyone I encountered was friendly and helpful. Hope your trip is amazing!

You’ll do fine!
Most portuguese people speak english.
Hope you have fun!

In Lisbon, it is rarely a problem not to be able to speak portugese. Even if you come across with people that can’t speak english, they immediately find somebody else who actually can! (happened to me a lot!)
If you also want to visit the suburbs of Lisbon, it is good to learn a few basics of portuguese.
Almost the same in Porto.
And a suggestion, portuguese people really appreciate if you speak even a few portuguese words. It is amazing and so sweet to see how they become happy by that.
I had lived near Lisbon for 6 months and had visited Porto and had so good time. I miss there and admire you a lot =)
If you want to ask more, please don’t hesitate.
Good voyage! =)

I did fine with a small phrase book. I think it’s not polite to assume other people speak your language, and you’re always best bumbling in theirs. If they actually can speak English, they’ll help you out right away.