Learn English – Early and earlier

Early means 'before a specified or expected time'.

earlier also means 'before a specified or expected time' and the specified or expected time can itself be an early time, in which case "earlier" means "more early". The reference time changes.

The meeting is at 7PM. Could you arrive early to help me set out chairs?

The meeting is at 7PM. Could you arrive an hour earlier to help me set out chairs?

Last week, you arrived at 6pm to help put out chairs for the 7pm meeting. Tomorrow, would you be able to arrive a little earlier, at 5:30, to help me set up the sound system too?

Both are correct. However, you might try, "Hello. May I speak with Sue, please?" Better is, "Hello, this is Tom Smith. Is Sue available to speak with?" (This is a matter of etiquette, not grammar.)