Use phone if you do not have enough money. Buy a power bank with it. If you do not really have light, get a second power bank so that you can charge the two at once when there is light. There are phone with 4000 to 5000 mAh battery that can last you almost a whole day with internet. If you can not get it new, get the second hand.
This na better advice you done give, this issue of light for naija no be today matter so the thing go better if him follow your advice buy power bank if him money no reach to buy two make him buy one first then latter if fit add another one. The price from 4000 to 5000 mAh go they between 4000-5000 naira to because 10, 000 mAh na 8000 naira, the thing no too cost if the person get the money make him just buy am to aviod disappointment from nepa.
I don't think it is every Bitcoin activity that can be done with a phone. There are people mining Bitcoin in Nigeria even on low key, there is no way such people will not need stable electricity. When power is made constant in Nigeria, a lot of businesses will boom including mining of Bitcoin.
If it is other areas of Bitcoin generating businesses like the forum, trading and others, then a phone is fine for it. Beyond that, a laptop is definitely needed.
Minning in Nigeria go get a lot of problems for rood the thing they consume light and light no stable, if na solar the person go spend spend because installation of solar no be play for Nigeria, and for some weeks now light done better sha but the thing no mean say they no go carry am but the thing go sweet if them go increase our light for this country, because plenty businesses need light without light many of this businesses go suffer.