Hi @Anonymous,
How does the event body look like? What’s the column type of the MR# in SharePoint list?
I have made a simple flow for your scenario, please take it for a reference.
The event body contains just a MR#, and the MR# in the SharePoint list is of type Single line of Text.

Note: To get the unique MR# in the event body, make sure the MR# is always placed in the same place so that you could extract them from the body properly. And let's say that the MR# are in the same length.
And for testing, I used the trigger “When an event is added, updated or deleted”, you could change it to the trigger “When an event is coming soon” on your side.
Then use the action Html to text to convert the email body to plain text.
In action Compose, use the following function:
length(body('Html_to_text'))
In action Compose1, use the following function:
add(indexOf(body('Html_to_text'),'MR#:'),4)
In action Compose2, use the following function:
substring(body('Html_to_text'),outputs('Compose_2'),sub(outputs('Compose'),outputs('Compose_2')))
Then Get items from SharePoint list.
Add a Condition to check if the items from the list contains the unique number returned from Compose3.
If yes, send Text message(SMS).

Best regards,
Mabel Mao