Apple (AAPL -0.37%) stock has had a rough run this week, falling about 6% at the time of this writing. Bearishness in the stock price was isolated to the last two days of the week as several analysts warned of weaker-than-expected iPhone sales. With iPhones accounting for 62% of trailing-12-month revenue, it's easy to see why any downward revisions for iPhone sales estimates could worry investors.

With Apple's fiscal 2018 second-quarter earnings report scheduled for May 1, iPhone sales are about to come into focus. Investors will not only get to see iPhone sales for Apple's second quarter, but they'll get some insight into how the key product line is faring today by looking at Apple's guidance for third-quarter revenue.

But could this sell-off in Apple shares be a buying opportunity?

iPhone X, Apple Watch, and Airpods charging on Apple's AirPower mat.

Apple products. Image source: Apple.

Reducing forecasts

On Thursday, analysts from Merrill Lynch and JPMorgan Chase both expressed concern about Apple's iPhone sales after Apple supplier Taiwan Semiconductor (TSM 1.01%) reported worse-than-expected guidance, saying, "Weak demand from our mobile sector will negatively impact our business despite strength in cryptocurrency mining." Taiwan Semiconductor (TSMC) guided for second-quarter revenue between $7.8 billion and $7.9 billion. On average, analysts were expecting guidance for second-quarter revenue of about $8.8 billion. 

Weak guidance from TSMC prompted a more conservative outlook for iPhones from both analysts. "Given TSM's guidance, we could see some additional downside to iPhone units," said Merrill Lynch analyst Wamsi Mohan. JPMorgan Chase analyst Gokul Hariharan forecast iPhone sales for Apple's fiscal 2018 third quarter to be as much as 5 million units below a current analyst consensus estimate for 42 million to 43 million iPhones.

On Friday, Morgan Stanley analyst Katy Huberty similarly lowered her forecast for Apple's third-quarter iPhone sales (via CNBC). She now expects 34 million iPhone unit shipments during the period, down from a previous forecast of 40.5 million units. iPhone unit sales at this level would mean the segment returns to year-over-year declines, as Apple shipped 41 million iPhones in the year-ago quarter.

Since these lowered forecasts for Apple's iPhone sales would impact the company's third quarter and not the second quarter, any weakness in third-quarter iPhone sales would be reflected in Apple's third-quarter revenue guidance provided in its May 1 update.

A buying opportunity?

While reports of worse-than-expected iPhone demand for Apple's third quarter are definitely worth considering in any analysis of the stock, this is also a good time to remember that Apple stock is already priced conservatively. With a price-to-earnings ratio of 17 (lower than its already conservative price-to-earnings ratio of 18.5 earlier this week) and trailing-12-month year-over-year sales and earnings growth of 10% and 22%, respectively, a pullback could represent a time to consider buying Apple stock.

Even Huberty remains bullish on the stock after slashing her estimates for iPhone sales "materially." Not only does she have a $200 12-month price target on the stock, but she told clients that a further pullback in Apple's stock price after the company releases its second-quarter earnings release could be a buying opportunity.

For investors willing to hold Apple stock for five-plus years, the stock's pullback in the last few days may already be enough to merit buying the stock.