Please do not mine with your phone, they aren't made to handle heat the way a dedicated ASIC, GPU or literally any other piece of electronics is, and that is earning you less than nothing. You will kill it before you even earn $0.01 (I am being literal here).
https://bitcoinwisdom.com/bitcoin/difficulty you can put in mining hashrate and see the revenue at current difficulty rating. An Antminer S5 (which you could probably find for free at this point) would be equivalent to 144,375,000 phones hashing at the same time. You are correct, CPU and GPU mining is out, and even ASIC mining for BTC has become an expensive and risky endeavour, with failure of hardware more likely than ROI.
Building your own miner is not very realistic, as it takes huge amounts of capital and R&D. Even the pros struggle to compete with one another in terms of efficiency and hashrate. I would suggest checking out sidehack here on the forums and his developments, namely his most recent USB stick the "2 Pac" (and stay tuned for pod miners to come). It may not ever earn enough in BTC to break even, but it helps secure the network and is a good tool for learning. Used as a solo miner, it's like a lottery ticket.
If you are interested in investing in bitcoin mining as a business and way to ensure income, IMHO you need $100,000 minimum to invest in miners and a hosting facility with VERY cheap electricity (<$0.06/kWh) to even consider it these days. The risk of hardware failure is greater today than it's ever been, and the margins to be made on miners are lower than ever with the difficulty increases. So for us small players I don't feel that the risks justify the rewards, but to each their own.
