Broadly speaking, you can connect to an audio conference meeting in two ways:
Conferencing via an audio conference bridge: This involves meeting participants joining the audio conference via their phones, whether those are modern Android or iOS models or traditional phones like landlines. It relies on an audio conferencing bridge, which lets multiple users securely join a call.
Conferencing via a conference service: A conference call can also be made through the internet. It relies on VoIP (Voice over Internet Protocol) to connect participants. Many popular conferencing solutions, like RingCentral, use VoIP and include video conferencing as well.