If sftp is available on the remote server, the command to invoke it would be (drum-roll please):
It works just like almost any other CLI FTP program. Explaining all the things you can do with it is a bit large for a superuser answer, so just read its manpage.
Now, it would be a bit unusual for a system to be configured to forbid scp, but allow sftp. Not that it can't be configured that way, but most admins who block one block the other.
If you find yourself in that boat, then you can leverage the fact that ssh lets you execute remote commands via any archive or copy program that will work with stdin and stdout. For example:
tar -c <files or directories to archive> | ssh user@host tar -x
dd if=file.to.transfer | ssh user@host dd of=destination.file
This works because if these programs don't have a file specified, they default to stdin or stdout as appropriate. So you create an archive or slurp a file and dump the result to stdout, and then you pipe that stdout to the stdin of ssh, which is running a program that will convert it back into the files you want.
Depending on your network conditions and file characteristics, you may want to invoke the sftp or ssh portions of these commands with -C to compress the traffic so it doesn't take as long.