Trouble Exporting iMovie

My iMovie has trouble exporting. I am using an iPhone SE with iOS 11.2.5 and I have a 16 GB with 13.8 GB used. I have deleted all my pictures and apps and have only saved the videos that I used in my iMovie. I bought more iCloud space but the video will not export to Google Drive due to "insufficient phone storage." I do not know what to do, therefore any help will be beneficial. I need it for my YouTube and I am unable to upload anything more than 15 minute video from my iPhone to YouTube. I am on a deadline and all help will be appreciated.