What's the easiest, least painful way to do this such that I can use it across computers?
Ideally something that would still let it work offline too, if needed. If it works on my phone too, would be nice.
My python knowledge isn't that deep so can't do anything too complicated
Then you could wrap it up in a website using django or another small web framework with an html form to upload the text file, process it using the same script and output the result as html. Then it becomes available on all devices with a web browser.
But if you mean message queue, you could create a python script that parses the text file using regex and place messages in a AWS SQS queue.
Simplest way to use across computers would be just to transfer the script to each computer you use.
The most simple way in this cade would be using an existing service with python-bindings. Todoist for example is a good service with a proper python-libary.