I'd like to know when I want to say the product is very old school and we are very hard to find it in the market......I should say this product has faded out or this product has phased out?
What's wrong with...
The product is fading out.
According to the free dictionary:
1. To disappear gradually.
2. To cause to disappear gradually. Used of a cinematic or television image or of a sound.
According to the Cambridge online dictionary:
fade (sth) out phrasal verb
If the picture or sound of a film or recording fades out or someone fades it out, it becomes gradually weaker.
I found 56 entries for 'fading out' on COCA, 15 on BNC, such:
... I'm not fading out . I mean, I don't want to make any dramatic breaks...
...so I start with a wash of cadmium orange fading out from the horizon upwards.
... to avoid is swaying backward and forward so that you are alternately bellowing and whispering, fading out or disappearing entirely at intervals like a badly tuned radio station!
still not ringing a bell for me.
even so, the bell is not ringing on this side of the pond.
Perhaps you can say that its use has faded out, but I wouldn't say it about the product itself.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.