Put them on a USB, your phone may not have the correct file format for the transfer. It is like going from a FAT32 to a FAT16, it won't work. The file table needs to be the same or compatible.
It's 800+384 when using a USB thumb drive you can drag the picture over the folder icon then drop in that drive. Then right click on it and left click edit.then in the upper left corner click on resize.then click on pixels and leave it on aspect ratio.Then say the picture was 1026 by 900 adjust the 1026 to where it's below 800 and the aspect ratio adjusts the 900 below 384 then it will download your up to32 pictures onto your wallpaper.I just went through this myself.