Executives at Pacific Investment Management Company hit the phones Monday in a campaign to persuade clients to stick with the firm, even as Wall Street traders placed bets against its holdings, seeking to exploit the sudden departure of co-founder Bill Gross.

Pimco executives, among them chief executive Douglas Hodge and the firm's new portfolio management team, hosted a string of calls with financial advisers at Wall Street firms, including Merrill Lynch and Morgan Stanley, to explain why the firm will thrive despite Gross's exit, according to people familiar with the matter.