Good resource
We used this book before and during our volunteer trip to Kenya.
It's a great resource, helps a lot, has all the basic things you wanna know (actually much more than you're going to need for a short trip), as well as slangs and even a few surprises (what to say in very specific situations, like when you're drunk or having sex (I'm guessing if they put this on the book, it must be because people asked for it)).
There are a few phrases they recommend I found out nobody uses anymore, and a few others that are used by people in the coast, but not by people in Nairobi area or other parts of the country, for example.
But still, I recommend it.
It's very small, fits in your pocket.
But there's so much information you really need to do your homework, study it before your trip, and mark the pages that interest you.

Swahili: Lonely Planet Phrasebook
For a compact book on Swahili this is the best I've seen. The contents of this little gem were easily divided into useful and practical sections, covering a broader use of the language than I've come across in other similar type books. Each section was uniquely and clearly identifiable allowing faster access to put your fingertips on the words or phrases you need. This book also succeeds in helping the reader obtain a basic yet concrete understanding of the Swahili language where other similar books have attempted but failed.

Very well built up - simple to use!
This course to teach yourself Swahili is easy for anybody - all you need is to take time and study.

Great comprehensive resource
This small hand-sized book is an excellent resource. Sections are seperated by practical categories (like food, social, and practical). Very easy to read, and really has everything you would need to get around.

Great book to have!
I had this guide when I went to Kenya, and I highly recommend it! It was very useful when I got very ill and needed to explain to a Swahili speaking doctor what was wrong with me. I also used it when I'd go to the Masai Markets and I always got a much better deal when I'd barter in Swahili. The Kenyans can speak English, but they appreciate it when you try to speak to them in Swahili.

I loved this guide so much I am buying copies for the members of my family who will be joining me for a holiday in Kenya this coming year.

It's an absolute must for any traveler!