What do I do?

Hi, and welcome to the Apple *user-to-user) Community.

Re: "When I try making a video on my phone no sound comes out".

Wondering if this is video you shoot from the camera,

(Eg: You can check your settings: Settings  > Camera > Record Video.

How to: Record videos with your iPhone camera – Apple Support )

or

a video you make with an app, (if so: which app ... eg iMovie / Clips)

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Re: "little volume image at the bottom of the screen? Well mine is gray with a line going through it".

Maybe tapping the greyed volume image will turn audio back on ?

or

Seems the video may have been recorded without sound

or

access to audio may not have been "allowed" for the app (eg: privacy)

or

the video is "muted" by another setting

Also:

"Before apps (like social media) use the camera or microphone on your iPhone, they’re required to request your permission and explain why they’re asking".

Control access to hardware features on iPhone – Apple Support

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Also wondering which iOS version you have installed on your iPhone:

(About iOS 16 Updates - Apple Support says iOS 16.5 is the latest.)

Sometimes updating the iOS, or if already updated, restarting the iPhone can help restore things to order. (How to: Restart your iPhone)

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Re: what do I do?

If nothing above helps, you can reply with more info

or

You could try reaching out to iPhone Support:

(There's a "Get Support / start now" link (online chat, phone, eMail etc) at the bottom of their webpage... link below)

iPhone - Official Apple Support

All the best :-)