I think I see the problem. You changed the ssh port (like recommended) away from 22.
You could try this:
sftp://user:password@ExternalLinkToRaspberryDDNS:PortExternal:/directory/directory1/
Notice the extra : after PortExternal
If that does not work, you could use fstab and sshfs. An fstab line would look something like this:
user@ip.of.my.server:directory fuse.sshfs x-systemd.automount,noauto,rw,user,transform_symlinks,user=<username>,pass=<password>,port=<portonserver>,allow_other,default_permissions,uid=1000,gid=1000 0 0
I haven’t played with this at all, so I have no idea if it will really work.
For more info about fstab: Configuring fstab based Samba share mounts