IFTTT has support for Amazon Echo (and the Alexa assistant) through the Amazon Alexa channel. Some channels allow you to specify variables, known as ingredients, from a trigger which will be passed into the output event.
The Google Assistant channel supports recognising a phrase with a text ingredient (see the "Google Assistant triggers and actions" at the bottom of the page):
Say a phrase with a text ingredient
This trigger fires when you say “Ok Google” to the Google Assistant followed by a phrase like “Post a tweet saying ‘New high score.’” **Use the $ symbol to specify where you'll say the text ingredient
Alexa's trigger does not seem to mention anything about text ingredients:
Say a specific phrase
This trigger fires every time you say "Alexa trigger" + the phrase that you have defined. For instance, if you set "party time" as the phrase, you can say "Alexa trigger party time" to have your lights loop colors. Please use lower-case only. Neither German characters (Umlaute/Eszet) nor their long-form equivalents (ae, oe, etc.) are currently supported — support is coming soon.
Does the Alexa channel support ingredients at all, or must I preprogram every possible input I want?