"agreed to plan" is correct and usable in written English.
You can use it when two or more parties come to an agreement on a plan of action. For example: After a lengthy discussion, the both sides agreed to plan a course of action that would benefit everyone.
Given the persistent uncertainties, engineers recently agreed to plan for the worst contingency, the failure of A.S.R. to save the day, and the glades.
In a postmortem teleconference last week, the political directors from the foreign ministries of UK, France and Germany agreed to plan for the worse and marshal European political resources for a potential rearguard action lobbying in Congress.
Also, I have met with the heads of the targeted institutes, and together we agreed to plan a concerted path to share the sacrifices among the various institutes.
Councillors have agreed to "plan for the worst" by approving a council tax hike of 4.99% to help plug a funding shortfall of £65m.
If the ceasefire holds for seven days, the US and Russia have agreed to plan joint attacks on the Jabhat Fateh al-Sham group, which was previously known as the al-Nusra Front, and on IS.
Each detachment fought independently under the previously agreed to plan to surround and destroy the Loyalists.
Earlier this year, various government branches agreed to plans for roughly 1,000 systems to be installed throughout Mexico City.
Moscovici said he expected the UK to co-operate in agreeing to plans for taxing the digital economy by this summer.
When you haven't had a drink in nine months, you automatically agree to plans like these.
In February, the Security Council agreed to begin planning to send United Nations troops.
He tried to cancel the late-night concert, and only agreed to a planned recording going ahead as a "test".
