Here's a quote from today's Sunday Times article about some weird stuff going on in Qatar in the build-up to the World Cup:
‘I wonder if Gianni Infantino, the Fifa president who claimed in an outlandish press conference yesterday that “I feel African, I feel gay, I feel a migrant worker”, has any idea what life is like here at the coalface.’
If you are at the coal face you are where the real work is done, not where people just talk about it. The phrase stresses the necessity of doing something rather than just talking about it, contributing in an active way rather than at a theoretical level.
The expression comes from coal-mining industry. The coalface is the place inside a mine where the coal is cut out of the rock. The figurative use of the phrase dates from the mid-20th century.
Here are some examples of the phrase used in The Guardian:
*To work at Amazon is to spend your days at the coalface of consumerism.* (The Guardian)
“There aren’t enough women at the coalface of UK film-making.” (The Guardian)
“We don’t work at the coalface, we don’t work with the victims.” (The Guardian
You can hear the idiom used in various contexts in the Youglish link here.