function extractPhoneContext(numberToExtractFrom) {
	const indexOfPhoneContext = numberToExtractFrom.indexOf(RFC3966_PHONE_CONTEXT_)
	// If no phone-context parameter is present
	if (indexOfPhoneContext < 0) {
		return null
	}

	const phoneContextStart = indexOfPhoneContext + RFC3966_PHONE_CONTEXT_.length
	// If phone-context parameter is empty
	if (phoneContextStart >= numberToExtractFrom.length) {
		return ''
	}

	const phoneContextEnd = numberToExtractFrom.indexOf(';', phoneContextStart)
	// If phone-context is not the last parameter
	if (phoneContextEnd >= 0) {
		return numberToExtractFrom.substring(phoneContextStart, phoneContextEnd)
	} else {
		return numberToExtractFrom.substring(phoneContextStart)
	}
}
Extracts the value of the phone-context parameter of `numberToExtractFrom`,
following the syntax defined in RFC3966.

@param {string} numberToExtractFrom
@return {string|null} the extracted string (possibly empty), or `null` if no phone-context parameter is found.