See what Messages is actually holding
Settings → General → iPhone Storage → Messages breaks the total into Photos, Videos, GIFs and Stickers, Other and Documents. On a phone with years of group chats, the video figure alone is often several gigabytes.
The same screen offers Review Large Attachments, which lists every attachment across all conversations sorted biggest first. Swiping left deletes one; the Edit button lets you select many at once. This is the fastest route by a wide margin.
Deleting attachments from one conversation
Open the conversation, tap the contact name at the top, then scroll to the attachments grid and choose See All. Tap Select, pick what you want gone and delete. The messages stay; only the attachments go.
Useful when you want to keep a conversation intact but clear the video someone sent you eleven times.
Stop it accumulating again
Settings → Apps → Messages → Keep Messages, changed from Forever to 1 Year or 30 Days, deletes older conversations and their attachments automatically. iOS asks for confirmation and then reclaims the space immediately, which on a long-standing phone can be enormous.
Also on that screen: Audio Messages and Video Messages both have an Expire setting, defaulting to After 2 Minutes. If yours is set to Never, that is a steady leak worth closing.
Save anything you want to keep first
Deletion here is permanent and does not go through Photos → Recently Deleted, because these attachments were never in your photo library. Anything you want to keep must be saved to Photos before you delete the conversation.
In a conversation, press and hold an image and choose Save. In the attachments grid, Select then Save works on many at once. Do this before changing Keep Messages, because that setting deletes without a second chance.
What about iCloud Messages
If Messages in iCloud is on — Settings → your name → iCloud → Messages — your conversations sync across devices, and deleting an attachment on the iPhone deletes it everywhere. That is usually what you want, but it is worth knowing before you clear a decade of photos.
It also means the storage is counted against your iCloud allowance as well as your phone. Our iCloud storage guide covers that side.
Frequently Asked Questions
How do I delete iMessage attachments?
Settings → General → iPhone Storage → Messages → Review Large Attachments, then select and delete. It lists every attachment sorted by size.
Does deleting attachments delete the messages?
No, if you delete attachments individually. Changing Keep Messages to 30 days or a year deletes whole conversations and their attachments.
Can I recover a deleted attachment?
No. Message attachments do not go to Photos → Recently Deleted. Save anything you want to keep before deleting.
How do I stop attachments building up?
Settings → Apps → Messages → Keep Messages, set to 1 Year, and check that audio and video messages are set to expire.