How do I store a swipe pattern in a password manager?

I would suggest giving each phone a name, then for the password use the keys on the num pad to represent the dots to hit.

For example, if you have a swipe pattern in the shape of an L (starting on top left), your password would be 74123. If you go with every dot in a "Z" shape (starting on top left), the password would be 789654123.

Most can't store pictures, but that would be another option. Take a picture of dots or draw them out on Paint, then draw the lines showing the dots to hit. Then you can just name the file something to do with the phone it's for, then store it somewhere only you have access to.

Example of "Z" Shape as a picture

Number the dots 1-n like a phone key pad and record the sequence of numbers.