I have a friend who gave me this plant to look after. They were concerned it was dying and want me to bring it back. Can anyone tell me what it is? On closer inspection, it produces a sticky sap substance from branch and leaf. It’s about 7 ft tall and wispy. It is non-flowering and I believe it’s a tree verses a bush or shrub. The top roots look light tan, possibly a fungus?
It's a eucalyptus leaf ficus. They're quite hardy, though in Colorado you should bring it indoors in the fall. (Or it's a eucalyptus but I'm assuming you already know what a eucalyptus smells like.)
The ficus is cool because they have a process called guttation--basically a plant sweating process. They excrete extra moisture.
From the soil and root description, I think you may be overwatering. Try cutting down on watering. Too much watering can cause roots to die (the browning could be root rot from being too wet, check if you have soft roots). When roots die, there's less water coming up to the plant, which can cause some leaves to look dry/wilted. Less water should also help control fungus if it is infected (I can't say for sure from photo)
The strap-like leaves, sticky sap and the fact it is 7 feet tall in a pot point to the plant possibly being an Oleander (Nerium oleander) (I chose that link since it mentions the sap and underlines its toxicity). See if you can compare your plant with the many pictures of oleanders at various stages of maturity, compare the bark you see, possible dead flowers, fruit capsules and so on and give us some feedback.
Oleanders are heavy feeders and send out strong root systems so it could be your plant has simply outgrown its pot or exhausted the resources. Nothing much interferes with oleander since it is so poisonous despite having an attractive flower. If you have the authority, pull the plant from its pot, if it has formed a clump you could try to divide up the root and repot separate pieces, otherwise propagation is by cuttings. In all cases use disposable gloves and take very great care to avoid contact dermatitis. Otherwise just cut it back and it should re-grow.