You want the most amount of people to use your Alexa Skill, but if they find it difficult to launch your skill or you have complex slot values, it can be difficult for people to use your skill as your invocation model may need optimizing. This Alexa Skill, Phrase Tester, allows you to say a phrase and it will report exactly what Alexa heard in text form, either on your Echo Show/Spot's screen or in a card in the Alexa app.
Using the skill repeatedly for what you think is the same phrase could result in Alexa picking different phrases up - so you can add those to your interaction model as synonyms.
Recommended: if you use an Echo Show or Echo Spot, the spelling of the phrase will be displayed on the screen along with the locale language. If not, the skill will send a card with the phrase spelling on it to your Alexa app.
It's only a simple skill, but is really handy for quickly deciding which synonyms to use. Saying phrases out loud also allows you to gauge how easy and fluent they are to say, instead of just typing them in.
To open the skill, just say, "Alexa, open Phrase Tester and test a phrase". Alexa will then ask you what phrase you would like to test.