From the 8.2.5 notes:
Introducing Party Sync
During this PTR we’re experimenting with a new mode that makes it easier for players in a party to do quests and play together: Party Sync. When players activate Party Sync, everyone in the party becomes aligned to the same quest state, including phases. By mousing over a quest in your tracker, you can see who is on the quest, what their progress is, and who’s ready to turn in the quest. There’s something else we’re going to try out on the PTR, a “replay” quest feature. This will allow players who have already completed certain quests to replay those quests with their friends for rewards that are appropriate to their current level, regardless of the original level of the quest.
We’re also relaxing level restrictions on queueing for instanced content with your friends. This allows lower-level players to queue for content in their level range, and higher-level players can choose to join them by having their level scaled down while they’re in the instance. This feature will be available for dungeon instances for PTR Week 1, with PvP instances being flagged in the following weeks. Please note that unlike Timewalking, when your level is scaled down via Party Sync you will temporarily lose access to abilities and powers (such as Azerite traits) with requirements that exceed your reduced level.
It's been a bit more than a decade since CoH had this, but it will be really nice to be able to help someone without being out of phase.