I thought about this myself, but it makes no sense. If the Celtics are willing to trade 1 spot down and give the Suns Bender, then they were not interested in drafting Bender in the first place, which makes trading up a moot point for the Suns. The only way a team would move up is if they are sold on Bender but scared of the Suns picking him, the earliest possible team that fits that criteria being the Timberwolves at #5.
(I actually think a trade with the Timberwolves could happen, possibly something centered around #5 plus Shabazz Muhammed, a decent role player off the bench, for #3. Maybe even the underutilized Bjelica, who is a solid passing/shooting big that could fill that Jerebko/Olynyk/Mirotic-type role if used correctly. Bender makes too much sense for them from a positional standpoint, especially if they are sold on Rubio and don't want Dunn.)