The phrase "come up with a plan" is correct and usable in written English. You can use it when you are suggesting someone create a plan of action. For example, "Let's come up with a plan to tackle this project.".
Come up with a plan for that.
He has come up with a plan," Mr. Wang said.
"The government has to come up with a plan B".
So I had to come up with a plan.
Mr. Fox did indeed come up with a plan.
"That's why they've got to come up with a plan.
It has come up with a plan to shed assets in Germany to pacify the commission.
Ludwig does not simply clarify my doubts with English writing, it enlightens my writing with new possibilities
Simone Ivan Conte
Software Engineer at Adobe, UK