Your solicitor has most likely already explained to you the importance of a well maintained diary to
record any agreements, discussions and care issues that you may have.
OpenBook provides you with the ability to record a diary note. If the communication happened on your phone OpenBook would have also captured what was actually said and agreed, depending on your Operation Mode.
With any agreements that you make verbally it is good practice to briefly confirm what you agreed by sending a simple SMS and OpenBook will store that for you so you can present it if needed.