The phrase "high volume of submissions" means that there is a large number of entries, proposals or applications that have been received by a particular organization, group or individual. Full definition
Due to the high volume of submissions, we do not guarantee a response or take any responsibility for the materials received (by mail or electronically). (entrepreneurmedia.com)
Due to the high volume of submissions, API's desire to nurture a diverse community of expression, and our preference on occasion to designate particular articles for observances or series, accepted articles may not be published immediately and are scheduled at the discretion of the editor. (attachmentparenting.org)
Due to the high volume of submissions, we are unfortunately not able to provide individualized feedback. (sundance.org)