One hidden source of considerable emissions is technology manufacture. An iPhone 8, 256 GB model, releases 71 kg of CO2. That's 156.5 lbs., which equates to the tailpipe emissions of almost 8 gallons of gasoline. Most of that impact is from manufacture (80% to be exact). A new MacBook Pro 15" releases 366 kg (805.2 lbs) of CO2 over its expected lifecycle, which is actually down from 710 kg of CO2 over the 2013 MacBook Pro thanks to Apple changing their source of aluminum to hydro-smelted and recycled aluminum streams. What I'm trying to get at, is technology has reached a point where hardware upgrades have less impact on performance. If you need to upgrade your hardware, shop refurbished or used. There are plenty of previous gen devices out there that still run just fine. My iPhone 6s is just as fast as the current models in day to day use. As for battery life, new batteries are much cheaper and have much less impact than a new device (and yes, you can change the battery in an iPhone relatively easy, just need the right tools).
Sources for Apple product environmental reports:
iPhone 8 - https://images.apple.com/environment/pdf/products/iphone/iPhone_8_PER_sept2017.pdf
2018 MacBook Pro - https://www.apple.com/environment/pdf/products/notebooks/15-inch_MacBookPro_w_Thunderbolt3_PER_July2018.pdf
2013 MacBook Pro - http://images.apple.com/environment/reports/docs/15inch_macbookpro_retina_per_feb2013.pdf