I am looking for a phrase that describes a really crappy mobile phone, which has become so dysfunctional that it is ready to be thrown away
Let me explore some industrial terms that are applicable for equipment or manufactured products.
- Defective: self-explanatory
- Zero scrap value: Not worth keeping
- Negative scrap value: costs extra money to dispose
- Zero/negative salvage value: as in scrap value
- Deprecated: outdated
- Deteriorated: self-explanatory
- End of life: self-explanatory
- Expired beyond the bathtub curve: an industrial statistical term describing the phenomenon where badly made products fail-early, or normal products failing at end-of-life.
- junk yard: where scrapped products or equipment go
- junk bin: a database/log-book category for stuffs to be moved to junk yard.
- disposal contractor: self-explanatory
- dispositioning: making a decision about that to do with the defective stuff.
- past expiry date: self-explanatory
- hazardous material/equipment: self-explanatory
I am guessing your dad/brother gave you his old cell phone, and you wish to make very strong and offensive statement about that cell phone. Or you are trying to convince your wife to let you buy a new phone.
This piece of deteriorated junk is deprecated in functionality, has negative scrap value and is beyond salvage. It has deteriorated beyond its bathtub expiry date, that its continued use beyond its long past end-of-life is considered hazardous and therefore may invite lawsuits through inadvertent use by someone other than yourself. I am dispositioning it to the junk bin.
While technically defunct implies the phone is no longer functioning at all, to say "almost defunct" or "about to be defunct" will get your point across. I also suspect that if speaking in an informal, hyberbolic manner, you can get away without the modifiers, such as "D@#%ed this defunct phone, I can never get a signal."
I know this doesn't really 100% fit what you are looking for but it's pretty good: burner
The term "burner phone" is a slang that refers to cheap, disposable pre-paid cellular phones. Burner phones are often associated with illegal activities; however, people can use burner phones for legitimate temporary phone numbers.
I know the context is overly specific for what you're looking for - but if you refere to your phone as a burner people would get the idea that you could possibly chuck it at anytime.