The chances of your phone's battery being made using cobalt from the Democratic Republic of the Congo (DRC) are, as this chart using data cited in Statista's DossierPlus 'Mining Industry in Africa' shows, very high.
The country, ranked 166 out of 180 countries on Transparency International's 2022 Corruption Perceptions Index (with a score of just 20 out of a possible 100), and with an estimated one million people living in modern slavery as of 2018, also happens to be the world's largest producer of the metal key to lithium-ion battery production.
The use of child labor in the mining of cobalt in DRC is well documented, with the U.S. Department of Labor estimating that 40,000 children, some as young as 6 years old, work in the mines there.