I highly recommend using Teto's English voicebank in OpenUtau. This will allow you to type the lyrics as plain English words, and they'll automatically be converted to phonemes for the voicebank.
Kasane Teto download page (select English Voicebank CVVC)
kasaneteto.jp
OpenUtau download page
OpenUtau: Open singing synthesis platform / Open source UTAU successor
www.openutau.com
1. Set up OpenUtau
Download the correct version of OpenUtau for your computer. Assuming you're using windows, make sure to unzip the folder, then put the folder in somewhere like Documents (not program files)
2. Install Teto's Voicebank
Start OpenUtau. Go to Tools > Install Singer, and select the zip file for Kasane Teto.
3. Create project
Create a new track. Each track has three drop down menus. The first one is for the singer. Click on that and select Teto's Voicebank. The second one is for the phonemizer and it starts out saying DEFAULT. Click on that and go to EN, then select the Teto English phonemizer.
Click in the main area of the track to create a part, then double click the part to open the piano roll. You can make new notes here. Double click on a note to edit the lyrics. You can type in plain English words, and it'll automatically be converted for Teto English.